The study of all aspects of living matter is a constant source of information and stimulation of the greatest theoretical and practical importance. The very origins of organic chemistry are rooted in a desire for knowledge of the composition of living bodies and the products of their metabolism, and, ever since the birth of our science, the study of natural products has always remained one of its important concerns. The investigation of plant constituents has been of particular significance for the development of organic chemistry; it should be borne in mind that the plant kingdom accounts for much the greatest part of living matter on our earth-more than 99·9 per cent, in fact lMoreover, plants not only produce all the types of compounds found in the animal kingdom but also a number of special groups of organic substances, especially terpenoids, alkaloids, and glycosides. The varied chemical structure of the numerous, genetically related compounds of these groups, and the biological activity and practical importance of many of them have ever invited their closer investigation, and it may be said fairly that the systematic researches in these fields have contributed greatly to the finest traditions of organic chemistry, and to the present extent and variety of this science. In my opinion, it is the work on terpenes and steroids which was of the greatest importance in the development and shaping of organic chemistry. On the one hand, there is the classical unity of each of these groups, given by their simple composition, limited to the three basic organogenic elements, and by the uniformity of rules governing their structure; on the other hand, we have the great structural diversity and ubiquity of occurrence-it is these features which have made the terpene and steroid field an arena in which many minds active in our science have tried their strength. It was in research on substances of these two groups that the principal methods of structural analysis of organic compounds were devised and put to the test, especially the methods of controlled degradation; at the same time, it provided a powerful stimulus to the development of synthetic methods. Studies on the alicyclic terpenes, and on the whole steroid group, have been the source of our present ideas on the spatial structure of organic compounds. The whole of chemistry has profited from the valuable techniques developed in these fields for the isolation of individual substances from complex mixtures, their characterization and identification by physical constants. Let me recall particularly the determination of relations between chemical structure and physical properties, especially spectroscopic properties, which form such an essential part of organic chemistry today.